The invention relates magnetic materials comprising ceramics enabling to be baked at relatively low temperatures, inductance elements using the same, and a making method thereof.
In general, magnetic materials (ferrite) are ordinarily composed of iron oxide (Fe2O3) in a range of not exceeding 50 mol % and in a rate of considerably approximate thereto, e.g., 48 to 49.8 mol % and other metallic oxides, e.g., nickel oxide (NiO), copperoxide (CuO), zinc oxide (ZnO) and others of a little exceeding 50 mol % in total so as to be 100 mol % in the whole quantity. A known composition is Fe2O349 mol %, NiO 21 mol %, CuO 10 mol % and ZnO 20 mol % (JP-A-4-354314). A composition point of iron oxide 50 mol % and other metallic oxides 50 mol % in total is called as "Stoichiometry", and if being greatly off from the vicinity of the composition point, surplus components are isolated to cause heterogeneous phases so that unexpected abnormalities of electromagnetic properties and porcelain properties happen, and therefore components should be selected in the vicinity of the stoichometry.
However, in the vicinity of the stoichometry, if the above mentioned combinations are made, it is difficult to set a relative magnetic permeability .mu.i to be 15 or less, and if other elements are substituted, there are problems existing as unsolved that a sintering temperature increases, metals to be used as internal conductors are limited, or temperature characteristic of the relative permeability is markedly bad.
On the other hand, with respect to the magnetic materials, investigations are being made on decreasing the proportion of iron (Fe) than the stoichometry, and a proposal of setting the iron oxide to be b elow 44.5 mol % has been made in regard to materials to be used to magnetic cores (JP-A-8-339913), and with respect to laminated inductance elements, a further proposal of decreasing iron oxide to be near 45 mol % has been made (JP-A-4-93006).
However, there has not yet been known such a magnetic material where the mol rate of the iron oxide is more lowered so as to s et the relative permeability to be below 15, and the firing is possible at relatively low temperature as 920.degree. C. or less enabling to be co-fired with the internal silver conductor.
It is an object of the invention to provide such magnetic materials in which the relative magnetic permeability .mu.i is small, the firing temperature is around 900.degree. C. enabling to be concurrently fired with the internal silver conductor, and a temperature changing rate of the relative magnetic permeability .mu.i is considerably small.
Inventors of this patent application have made various studies on compositions of magnetic materials, and discovered that even if the mol percentage of the iron oxide is lowered than the stoichiometry, a magnetic material having a lower relative permeability and a low calcination temperature property may be obtained unexpectedly, and based on this discovery they have made the invention.
That is to say, the magnetic material of the present invention includes a ceramics having the composition in the range of Fe2O335.0 to 44.5 mol %, NiO 47.0 to 56.5 mol % and CuO 5.0 to 12.0 mol %, and having relative magnetic permeability of 15 or less; the inductance element comprising this magnetic material and the internal metallic conductor; and a method characterized by using, when making the laminated inductance elements by concurrently baking ceramic green sheets and internal metallic conductors, a substance to be used as the ceramic green sheet, which substance has the composition in the range of Fe2O335.0 to 44.5 mol %, NiO 47.0 to 56.5 mol % and CuO 5.0 to 12.0 mol %, and using a silver or silver alloys as the internal metallic conductor, and carrying out the firing at temperature of 880 to 920.degree. C.